1. Field of the Invention
The present invention relates to noise generators such as radar jammers utilizing voltage controlled oscillators.
2. Description of the Prior Art
In the prior art digital circuitry was used to generate orthogonal sequences of numbers which were converted by a digital to analog converter to a sequence of voltages. The voltage sequences were coupled to a voltage controlled oscillator (VCO) by a high speed analog switch. The voltage controlled oscillator would transform a sequence of voltages to a sequence of frequencies to provide a noise frequency spectrum. One example of digital circuitry used to generate a sequence of voltages to be applied to a voltage controlled oscillator for generating corresponding frequency spectrums was described in U.S. Pat. No. 4,056,788 issued Nov. 1, 1977 entitled "Digital To Analog Noise Generator" by Joel E. Brown and Kelly C. Overman and assigned to the assignee herein.
In U.S. Pat. No. 4,056,788 a sequence of voltages are applied to the input of a voltage controlled oscillator. Each voltage in the sequence, when applied to the VCO, would cause the voltage controlled oscillator to slue or shift to the new frequency wich required a certain amount of time depending upon how far the new frequency corresponding to the new voltage at the input was from the present frequency. The time required for the voltage controlled oscillator to slue or shift to the new frequency corresponding to the new voltage at the input and the time required for the voltage controlled oscillator to settle on the new frequency once the voltage controlled oscillator had slued to it was undesirably long causing an undesirable output of off frequencies during the interim. In other words, the oscillator would be providing a frequency output as it moved from its present frequency to a new frequency. And, once the voltage controlled oscillator reached the new frequency, its frequency would vary about the new frequency until the oscillator had settled or stabilized on the new frequency corresponding to a voltage at its input. The additional frequency outputs which occurred between desired frequency outputs resulted in lower quality signals or off frequencies from the voltage controlled oscillator.
It is therefore desirable to provide a noise generator that provides only the desired frequency outputs.
It is further desirable to provide a noise generator that lessens the requirements of slue rate and settling time of a voltage controlled oscillator utilized in the generator.
It is further desirable to have a high quality noise generator with means for interrupting the noise generated frequencies to provide a frequency output having a duration externally controlled.
It is further desirable in a noise generator to utilize a plurality of voltage controlled oscillators having outputs which may be switched to one or more of a plurality of output terminals.